Reionization on Large Scales III: Predictions for Low-ell Cosmic Microwave Background Polarization and High-ell Kinetic Sunyaev-Zel'dovich Observables

TL;DR

This paper predicts large-scale polarization and small-scale temperature anisotropies in the CMB caused by reionization, using simulations to model the epoch and forecast observational constraints from current and future experiments.

Contribution

It introduces a novel simulation-based method for modeling reionization effects on CMB anisotropies in large volumes, providing new predictions for the patchy kSZ power spectrum.

Findings

Patchy kSZ power at ell=3000 ranges from 0.6 to 2.8 μK^2.

Patchy kSZ amplitude scales with mean reionization redshift and duration.

Future CMB experiments can detect and constrain reionization parameters.

Abstract

We present new predictions for temperature (on small angular scales) and polarization (on large angular scales) CMB anisotropies induced during the epoch of reionization (EoR). Using a novel method calibrated from Radiation-Hydrodynamic simulations we model the EoR in large volumes (L >~ 2 Gpc/h) in the context of galactic reionization. We find that the EoR contribution to the kinetic Sunyaev- Zel'dovich power spectrum (patchy kSZ) ranges between ~0.6 - 2.8 muK^2 at ell = 3000, for the parameter space we explored. These patchy kSZ power spectra are calculated from large 15 Deg x 15 Deg maps that are found to be necessary. Decreasing the size of these maps biases the overall patchy kSZ power to higher values. We find that the amplitude of the patchy kSZ power spectrum at ell = 3000 follows simple scalings of D_ell=3000^kSZ propto <z> and D_ell=3000^kSZ propto Delz^0.47 for the mean redshift (<z>) of reionization and the duration (dz). Using the constraints on <z> from WMAP 7-year results and the lower limit on dz from EDGES we find a lower limit of ~ 0.4 muK^2 on the kSZ at ell = 3000. Planck will constrain the mean redshift and the Thomson optical depth from the low-ell polarization power spectrum. Future measurements of the high-ell CMB power spectrum from the South Pole Telescope (SPT) and the Atacama Cosmology Telescope (ACT) should detect the patchy kSZ signal if the cross correlation between the cosmic infrared background and the thermal Sunyaev Zel'dovich effect is constrained. We show that the combination of temperature and polarization measurements constrains both <z> and dz. The patchy kSZ maps, power spectra templates and the polarization power spectra will be publicly available.